INFRARED LINES FROM ACTIVE GALACTIC NUCLEI - A THEORETICAL APPROACH

We present theoretical results of prominent IR lines from AGNs. Composite models, which account consistently for photoionization and shocks, are used. Our aim is to provide theoretical data in view of comparison with observations. Fine-structure IR line ratios and IR-to-optical line ratios, which depend on temperature and density, are analyzed. It is found that the different combination of the shock velocity and of the intensity of the central flux may change line ratios by large factors. Particularly in the ejection case, the low-ionization lines depend on the geometrical depth of the clouds, not only on the shock velocity, the intensity of photoionizing radiation, and on its high-energy cutoff. The observational data of NIR line ratios from AGNs are compared to theoretical results, and the fitting is good enough to confirm the validity of composite models and, consequently, to provide more evidence for the presence of shocks in the NLR. At present, regarding the number of lines observed, the line spectra are too poor to permit a serious analysis of single AGNs.